The treatment of orthopedic injuries, such as bone fractures, usually involves immobilization of a portion of the body in a cast. Immobilization protects the injured body portion, maintains alignment of the bones and prevents further injury. Typical casting materials include plaster of paris or fibers impregnated with plaster of paris as well as newer casting materials such as Fiberglass and polyurethanes which are lightweight and waterproof.
Typically, the injured body portion is wrapped with cotton to provide a cast lining which protects the skin from the cast material itself. The cast lining has a cushioning effect and enables easier removal of the cast after the healing period is complete. Traditionally, cotton or hydrophobic synthetic fabrics have been used as a cast lining.
The use of cotton cast lining has the disadvantage that cotton absorbs and retains moisture and thus becomes soggy. For example, cotton cast lining absorbs perspiration or water introduced under the cast when the casted limb or body portion is immersed in water when swimming or bathing. Typically, the cast lining must be dried through the casting material or, alternatively, the total cast and lining must be removed and replaced, a difficult and time consuming process.
Additionally, cotton fibers are hollow and retain moisture in the cotton fabric; cotton even absorbs and pulls moisture from the air. This moist environment combined with heat generated from the casted body portion enables the growth of mildew and bacteria on the cast lining beneath the protective cast. Mildew and bacterial growth are the source of itching, rashes, unpleasant odor and infections.
Once cotton or a cotton-like liner becomes wet, it may, for all practical purposes, never dry out. This condition leaves the skin in a continual wet or damp state. The skin then starts to breakdown. Since the skin is the body's primary barrier against infection, skin breakdown allows microorganisms, such as bacteria and fungi, to invade the underlying tissue causing the skin and underlying tissue to macerate, i.e., undergo a softening and decomposition. Maceration of the skin can lead to complete loss of the healed condition in cases of a foot cast or serious damage and loss of proportions of the palm in cases of a hand/arm cast. Maceration also leads to local necrosis of the skin and subcutaneous tissues.
Cast liners have also been developed from hydrophobic polymers. U.S. Pat. No. 4,539,982 describes a flexible, odor-adsorbing web in the form of a sheet-like matrix containing open-celled or closed-cell foam or cellulosic fibers in a binder filled with activated carbon particles. The surface of this matrix which is in contact with the skin is a hydrophobic fiber layer which has preferably been needle-punched into the carbon containing matrix. The outer surface of the matrix may include a hydrophilic fiber layer, also needle punched into the foam matrix. In use, perspiration generated at the skin surface is wicked by the hydrophobic fibers into the foam matrix where the activated charcoal particles adsorb odor causing components. The aqueous components of perspiration are absorbed by the hydrophilic fibers and transported through the foam matrix to the space between the cast and the cast lining. This structure is expensive and does not sufficiently remove moisture from beneath the cast and wick the moisture to the outside to dry. It has the further disadvantage of having a hydrophobic fiber layer in contact with the skin causing some discomfort during use.
U.S. Pat. No. 4,516,572 describes a perforated closed-cell padding material for use as a cast lining. The padding material is substantially non-wettable by either water from the surrounding environment or by perspiration. The padding material is permeable to water by virtue of the perforations which allow water vapor transmission through the holes into the atmosphere. The smoothness of the padding material allows trapped water to actually run down and out the end of the cast along the skin. Trapped moisture is transported by the perforations in the padding material when the outside of the cast is heated with a hair dryer, for example. Although an improvement over cotton cast lining, this padding material retains substantial amounts of water unless the cast lining is dried by heating, a time consuming and difficult process as noted above.
Hydrophilic polymers have been used as artificial skin materials and for wound coverings in which a moist environment is maintained around the wound. Wounds resulting in total or partial destruction of the epidermal skin layer such as second and third degrees burns, severe abrasions, ulcers and donor sites for skin grafting are typically covered with these materials in order to keep the wound hydrated and promote healing. These hydrophilic materials adsorb fluids exuded from wounds allowing evaporation of excess moisture while maintaining a generally moist environment around the wound. Such materials are described by U.S. Pat. No. 2,858,830; U.S. Pat. No. 4,554,317 and U.S. Pat. No. 5,098,500.
Hydrophobic cast linings are inferior in their ability to transport moisture from under a cast to the outside environment. Hydrophilic materials which adsorb moisture to maintain a moist environment are unsuitable as cast linings where it is desirable to maintain a dry environment beneath the cast. A need continues to exist, therefore, for improved cast lining materials.